1. Field of the Invention
The present invention relates generally to charged particle beam systems. More particularly, the present invention relates to an improved calibration sample for use in charged particle beam systems, such as electron beam systems and ion beam systems.
2. Description of the Background Art
Previous techniques for calibrating electron beam systems typically use silicon chips either with a patterned layer of material (typically oxide or gold), or deposited with specimens having naturally occurring patterns (such as fine metal grains). Disadvantageously, as a result of repeated exposure to electron beams, organic contamination frequently builds up on the surface of the silicon chip. Such a contamination layer may degrade the quality of the calibration image over time, resulting in variations in the calibration results and/or the need for periodic replacement of the calibration sample. Another disadvantage is that the contrast of these calibration samples is a function of the energy of the electron beam. As a result, systems that need calibration at multiple beam energies may have difficulty being calibrated due to the changing (or even inverting) contrast at different energies.
Gold grid calibration samples have also been used. Such grids may be made by punching a fine array of holes in gold foil. However, gold grids lack the fine features and sharp edges necessary to perform certain types of calibrations.